Placental Territory Discordance Research Articles

Thick artery–artery anastomoses delay the onset of selective fetal growth restriction in monochorionic diamniotic twins: a 7-year single-center cohort study

ObjectiveThis study aimed to investigate differences in placental characteristics between early- and late-onset selective fetal growth restriction (sFGR) in monochorionic diamniotic twins.MethodsA total of 253 patients with sFGR between April 2013 and April 2020 were retrospectively analyzed. Placental characteristics of early- and late-onset sFGR were compared.ResultsThe gestational age at diagnosis and delivery in the early-onset group was significantly less than that in the late-onset group [22.0 (16.9–23.9) and 28.4 (24.0, 36.3) weeks, P < 0.001; 33.1 ± 2.2 and 33.7 ± 2.5 weeks, P = 0.025]. The birth weight of normal growth and growth-restricted fetuses in the early-onset group was less than the late-onset group [1,990 ± 422 and 2,162 ± 525 g, P = 0.044; 1,320 ± 409 and 1,595 ± 519 g, P = 0.001]. The birthweight discordance ratio in the early-onset group was greater than the late-onset group (0.34 ± 0.12 and 0.29 ± 0.13, P = 0.001). The early-onset group had a significantly lower prevalence of sFGR type I than the late-onset group (37.5 and 62.0%, P = 0.018). The early-onset group had a significantly higher prevalence of sFGR type III than the late-onset group (30.4 and 12.7%, P = 0.048). The early-onset group had a lower prevalence of thick artery–artery anastomoses than the late-onset group (37.5 and 62.0%, P = 0.006). The placental territory discordance ratio in the early-onset group was higher than in the late-onset group [0.60 (0.01, 0.80) and 0.50 (0.01, 0.88), P = 0.018].ConclusionUnequal placental territory is the cause for most of the late-onset sFGR. Thick artery–artery anastomoses may delay the onset time of these cases of sFGR.

Comparison of pregnancy outcomes and placental characteristics for monochorionic diamniotic twins with and without proximate umbilical cord insertion

IntroductionThis study was developed to evaluate the relative placental characteristics and pregnancy outcomes associated with monochorionic diamniotic (MCDA) twins with and without proximate umbilical cord insertion (PCI). MethodsAll MCDA twins delivered with complete placentas for whom placental characteristics were assessed via dye injection between April 1, 2013 and April 1, 2021 were included in the present cohort study. Cases were separated into PCI and non-PCI groups, and pregnancy outcomes and placental characteristics were then compared between these groups. ResultsBirthweight discordance rates were significantly lower in the PCI group relative to the non-PCI group (7.3 ± 7.5% vs 29.9 ± 16.8%, P＜0.001), while relative to the non-PCI group, rates of artery-artery (AA), vein-vein (VV), thick AA, and thick VV anastomoses were significantly higher in the PCI group (95.5% vs 67.0%, P = 0.008, 59.1% vs 16.4, P＜0.001,90.5% vs 34.9%, P＜0.001, 54.5% vs 10.5%, P＜0.001). Significantly more anastomoses were observed in the PCI group (7 (3,11) vs 6 (3,15), P = 0.015), and they were significantly larger on average than those in the non-PCI group 12.8 (6.7,21.3) mm vs 11.9 (3.4, 24.6) mm, P = 0.009). Significantly lower placental territory discordance and UCI ratios were evident in the PCI group relative to the non-PCI group (23.5 (15.0,51.0) % vs 60.0 (2.0,80.0) %, P＜0.001, 13.3 ± 5.8% vs 56.1 ± 18.0%, P < 0.001). Marginal cord insertion rates were lower in the PCI group relative to the non-PCI group (13.6% vs 77.5%, P < 0.001). DiscussionThe placental structure of MCDA twins with PCI is distinct from that of twins without PCI, and these results suggest PCI may be indicative of the more even distribution of placental territory between MCDA fetuses.

A study on the correlation of placental characteristics and the onset of selective intrauterine growth restriction.

To investigate the correlation between placental characteristics and the onset of selective intrauterine growth restriction (sIUGR) and to explore the influence of placental characteristics on sIUGR onset. A retrospective cohort study was conducted at our hospital from April 2013 to April 2019. The pregnancy data and placental perfusion of 114 sIUGR patients who had received conservative treatment and delivered in our hospital were included. Correlation analysis was conducted between the total diameter of placental anastomoses, placental territory discordance, umbilical cord insertion point distance ratio, and the onset time of sIUGR. The prevalence of AA anastomoses was 88.6% (101/114), with an average total diameter of 2.8 ± 1.5 mm, the prevalence of AV anastomoses was 93.9% (107/114), with an average diameter of 5.4 ± 3.6 mm, and the prevalence of VV anastomoses was 18.4% (21/114), with an average diameter of 4.0 ± 1.9 mm. There was a significant negative correlation between the time of sIUGR onset and the placental territory discordance ratio with a Spearman correlation coefficient of -0.306 (P = 0.001). The larger the placental territory discordance, the earlier onset time of sIUGR.

Placental characteristics in different types of selective fetal growth restriction in monochorionic diamniotic twins.

This study aimed to explore the differences in placental characteristics among three types of selective fetal growth restriction (sFGR) in monochorionic diamniotic twin pregnancies. A total of 123 placentas with sFGR between April 2013 and October 2019 were retrospectively analyzed after dye injection. Placental characteristics were compared among the three types. The gestational age at diagnosis and delivery was less in sFGR II and III than in sFGR I (22.9 [21.7-33.6], 23.3 [20.0-26.1] and 25.7 [19.0-35.0] weeks, p<0.001; 32.3 [31.6-35.1], 34.1 [29.9-34.7] and 35.5 [34.0-37.0] weeks, p<0.001). The birthweight discordance ratio was less in sFGR I than in sFGR II (0.28 [0.14-0.43] and 0.30 [0.23-0.37], p<0.001). The prevalence of a thick artery-artery anastomosis was higher in sFGR III than in sFGR I or II (81.8%, 44.9% and 48.6%, p=0.010). The placental territory discordance ratio was higher in sFGR II and III than in sFGR I (0.60 [0.17-0.88], 0.60 [0.01-0.80] and 0.50 [0.01-0.71], p=0.001). Compared with sFGR I, the earlier onset time of sFGR II and III might be due to their higher placental territory discordance. The prevalence of thick artery-artery anastomoses was expected to be higher in sFGR III than in sFGR I or II.

Comparison of the ratio of placental territory discordance to birthweight discordance in placentas of monochorionic diamniotic twins.

The ratio of placental territory discordance to birthweight discordance was calculated in monochorionic diamniotic twin placentas. We then determined whether the ratio: (1) correlated with the overall diameter of the placental superficial vascular anastomoses and (2) was different in normal monochorionic diamniotic twin (normal MCDA), twin-to-twin transfusion syndrome (TTTS), and selective intrauterine growth restriction (sIUGR) pregnancies. A prospective study of MCDA placentas was conducted from April 1, 2016, to April 1, 2019, including three groups, normal MCDA (N = 49), TTTS (N = 38), and sIUGR (N = 52). Placentas were studied via dye injection. In the normal MCDA, sIUGR, and TTTS groups, the ratio positively correlated with the overall diameter of the placental superficial vascular anastomoses (Spearman's = 0.295, 0.619, and 0.530; p = 0.040, <0.001, and 0.001, respectively) and gradually decreased from normal MCDA to sIUGR and to TTTS (2.88 (0.34, 64.25), 1.70 (0.27, 4.52), and 1.03 (0.12, 15.17); p < 0.001, p = 0.016/<0.001/0.005, respectively). The placental territory discordance to birthweight discordance ratio is an effective index reflecting the overall vascular anastomoses in MCDA placentas.

Effect of placental vascular distribution on residual anastomoses after fetoscopic laser surgery for twin to twin transfusion syndrome

Objective: To investigate the effect of placental vascular distribution on residual anastomoses (RA) after fetoscopic laser occlusion of chorioangiopagous ressels (FLOC) for twin to twin transfusion syndrome (TTTS). Methods: A total of 57 cases of TTTS after laser surgery were retrospectively analyzed from April 2014 to April 2019 in Peking University Third Hospital. The patients were divided into RA group (24 cases) and non-RA group (33 cases) according to whether RA occurred in the placenta after laser surgery. The clinical characteristics, perioperative conditions, pregnancy outcomes and placental structure characteristics of the two groups were compared. Multivariate logistic regression was used to analyze the risk factors of placental vascular distribution for RA. The RA group was further divided into non-remission group and remission group, and the placental characteristics and pregnancy outcome of the two groups were compared. Results: (1)General clinical characteristics: the age, application of assisted reproductive technology, incidence of gestational hypertension, gestational diabetes mellitus, preoperative maximum amniotic fluid depth of the donor and recipient twins, Quintero stage and placental position of TTTS patients in the two groups were compared respectively, and there were no statistically significant differences (all P>0.05).The gestational age of patients received FLOC in the RA group was significantly higher than the non-RA group [(23.0±2.4) vs (21.9±2.7) weeks, P=0.033].(2) Perioperative conditions and pregnancy outcomes: the delivery gestational age of the RA group was significantly lower than that of the non-RA group (median:31.8 vs 34.4 weeks, P=0.002);The newborn birth weight in the RA group was significantly lower than that in the non-RA group [(1 648±597) and (2 013±481) g, P=0.003].The birthweight difference in the RA group was significantly higher than that in the non-RA group (median:0.30 vs 0.11, P=0.005). (3) The placental structure and the risk factors influencing RA happened: the differences in the proportion of four types of placental vascular distribution in the RA group and non-RA group were different significantly (χ²=10.214, P=0.012), with a detail of parallel type 29% (7/24) and 3% (1/33), staggered type 58% (14/24) and 76% (25/33), hybrid 8% (2/24) and 21% (7/33), monoamniotic membrane type 4% (1/24) and 0 respectively. Multivariate logistic regression analysis showed that parallel placental vascular distribution was an independent risk factor for RA after FLOC (OR=24.5, 95%CI 1.7-336.2, P=0.017). (4) Placental characteristics and pregnancy outcomes in the remission and non-remission groups of the RA group: the incidence of three kinds of anastomoses, the total number, total diameter and proportion of RA, and the placental territory discordance ratio were compared between the two groups, and there were no statistical significances (P>0.05);The birth weight difference ratio in the non-remission group was higher than that in the remission group (median:0.41 vs 0.28, P=0.036). Conclusion: The parallel type of placental vascular distribution may be an independent risk factor for RA in TTTS after laser surgery.

Pregnancy outcomes and placental characteristics of selective intrauterine growth restriction with or without twin anemia polythemia sequence

IntroductionTo investigate differences in the pregnancy outcomes and placental characteristics of selective intrauterine growth restriction (sIUGR) with or without twin anemia polythemia sequence (TAPS). MethodssIUGR patients were assigned into two groups based on the occurrence of TAPS. The pregnancy outcomes and placental characteristics were compared. A diameter of ≥2 mm was defined as thick anastomosis. ResultsThe prevalence of artery-to-artery (AA) (45.5% vs 88.6%, P = 0.002) and thick AA (0% vs 53.5%) in TAPS group were lower than non-TAPS group. The overall diameter of AA (0.5 (0.4–1.3) vs 2.5 (0.3–7.1) mm, P = 0.001) in TAPS group was smaller than non-TAPS group. The prevalence of thick artery-to-vein (AV) (0% vs 36.0%) in TAPS group was lower than non-TAPS group. Also, the overall diameter of AV (0.9 (0.6–2.1) vs 4.8 (0.3–17.8) mm, P < 0.001) in TAPS group was smaller than non-TAPS group. The total quantity (2 (1–6) vs 6 (1–16), P = 0.001), and the overall diameter of anastomoses (1.1 (0.6–4.7) vs 7.5 (0.5–22.4) mm, P < 0.001) were smaller in TAPS group than non-TAPS group. The placental territory discordance ratio of TAPS group was smaller than non-TAPS group (0.39 (0.13–0.56) vs 0.56 (0.01–0.88), P = 0.008). The umbilical cord insertion distance ratio in TAPS group was higher than non-TAPS group (0.81 ± 0.12 vs 0.57 ± 0.20, P < 0.001). DiscussionThe placental anastomoses of sIUGR with TAPS were small. sIUGR with TAPS had smaller differences in placental share and larger distances between umbilical cord insertions.

Comparison of placental characteristics of twin-twin transfusion syndrome with and without selective intrauterine growth restriction

Objective To explore differences among placental anastomoses, territory discordance, and umbilical cord insertion of twin-to-twin transfusion syndrome (TTTS) with and without selective intrauterine growth restriction (sIUGR). Methods This study retrospectively analyzed 57 patients with TTTS who received conservative treatment and finally delivered at the Department of Obstetrics and Gynecology of Peking University Third Hospital from April 2014 to April 2019. Nine of the patient’s placentas were too broken to finish the perfusion, and 48 were kept for graph analysis after perfusion. Among the 48 placentas, there were 17 in the TTTS with sIUGR group and 31 in the TTTS without sIUGR group. Differences in the placentas were compared between groups. Results The birth weight discordance ratio in the sIUGR group was significantly higher than that in the non-sIUGR group (0.41 ± 0.20 vs 0.24 ± 0.15, p = .001). The prevalence of thick artery-artery (AA) anastomoses in the sIUGR group was significantly higher than that in the non-sIUGR group (35.3% vs 6.5%, p = .017). The placental territory discordance ratio in the sIUGR group was significantly higher than that in the non-sIUGR group (0.40 [0.05, 0.86] vs 0.25 [0.02, 0.67], p = .024). The prevalence of velamentous cord insertion in the sIUGR group was significantly higher than that in the non sIUGR group (35.3% and 6.5%, p = .017). Conclusions Placental territory discordance and velamentous umbilical cord insertion may be causes of TTTS with sIUGR. Compared with TTTS without sIUGR, TTTS with sIUGR had a higher prevalence of protective AA anastomoses in the placenta.

Study of the placental characteristics and time of onset of twin-to-twin transfusion syndrome

IntroductionTo investigate the correlation between placental superficial anastomoses, placental territory and the umbilical cord attachment site with the time of onset of twin-to-twin transfusion syndrome (TTTS), and to explore the influence of placental characteristics on the time of onset of TTTS. MethodsA retrospective analysis was performed on 48 cases of TTTS managed conservatively at the Obstetrics Department of Peking University Third Hospital from April 2014 to April 2019. Placental superficial anastomoses, placental territory, the distance between the insertion points of the umbilical cord were measured after placental dye injection. Correlation analysis was conducted between placental characteristics and the time of onset of TTTS. Results(1) The incidence of AA anastomoses was 33.3% (16/48) with a mean total diameter of 2.3 ± 1.4 mm, that of AV anastomoses was 95.8% (46/48) with a mean total diameter of 1.2 ± 0.4 mm, and that of VV anastomoses 22.9% (11/48) with a mean total diameter of 2.3 ± 1.1 mm (2) The time of onset of TTTS was positively correlated with the umbilical insertion ratio (Spearman correlation coefficient = 0.404, P = 0.004), but not correlated with the total diameter of anastomoses in the three different types, or with placental territory discordance. DiscussionThe time of onset of TTTS was positively correlated with the umbilical insertion ratio, which suggest that the distance between umbilical cord insertion sites may affect the time of onset of TTTS. The smaller the distance between the umbilical cord insertion sites, the earlier the time of onset of TTTS is likely to be.

Clinical outcome and placenta characteristics of spontaneous twin anemia-polycythemia sequence

Objective: To investigate the clinical outcome and placental characteristics of spontaneous twin anemia-polycythemia sequence (sTAPS). Methods: Twelve cases with sTAPS delivered in Peking University Third Hospital from May 2013 to August 2016. The data of ultrasound characteristics, gestational age at delivery, and 1 minute Apgar score were analyzed, retrospectively. Placental superficial vascular anastomoses, placental territory discordance and the ratio of umbilical cords insertion distance to the longest placental diameter were also analyzed. Results: (1) Only 1 case of sTAPS was diagnosed prenatally, the others were diagnosed postnatally because the fetal middle cerebral artery(MCA) doppler was not measured regularly. Five cases were complicated with selective intrauterine growth restriction (sIUGR). The median gestational age at delivery was 32.8 weeks (31-37 weeks) . The pregnancies were terminated because 3 cases were sIUGR type Ⅰ, 1 case was sIUGR type Ⅱ, 1 case was sIUGR type Ⅲ, 2 cases were fetal distress, 2 cases were severe pre-eclampsia, 2 cases were premature rupture of membrane, 1 case was fetal hydrops with abnormal doppler waveforms of ductus venouses. (2) When 5 sIUGR cases were excluded, there was no difference between the twins in birth weight [1 797 g (940-2 620 g) , 1 648 g (980-2 500 g) ; P=0.688]. The hemoglobin (Hb) level in all donor was significantly lower than recipient (P=0.000) and the inter-twin Hb difference was 147.6 g/L (84.0-216.0 g/L). While the reticulocyte percentage in donor was significantly higher than recipient (P=0.013) and reticulocyte percentage ratio was 3.60 (1.04-7.50). Five donor newborns had neonatal asphyxia, including 1 severe asphyxia, while no asphyxia happened in the recipient twins. (3) Arterio-arterial (A-A) anastomoses, veno-venous (V-V) anastomoses, arterio-venous (A-V) anastomoses were found in 3, 1 and 11 placentas, respectively. The total number of anastomoses was 2 (1-5) and the total diameter was 1.1 mm (0.4-2.1 mm), including 0 (0-1) A-A anastomoses with 0.2 mm (0.0-0.9 mm) in diameter and 2 (0-5) A-V anastomoses with 0.7 mm (0.0-2.1 mm) in diameter. The placental territory discordance was 0.17 (0.02-0.40) and the ratio of umbilical cords insertion to the longest placental diameter was 0.82 (0.34-0.99). Conclusions: The pathogenesis of sTAPS might result from slow and chronic blood transfusion from donor to recipient through a few minuscule vascular anastomoses in the placenta. In all monochorionic twins, especially sIUGR cases, MCA doppler should be monitored closely in the second and third trimester, in order to diagnose and manage sTAPS in time.

Placental characteristics of twin-to-twin transfusion syndrome

To explore the prevalence, number and size of anastomoses, placenta sharing and placental cord insertion in twin-to-twin transfusion syndrome (TTTS). A total of 97 monochorionic placentas were collected from June 2013 to June 2014 during fetoscopic laser surgery or selective feticide. After eliminating 23 placentas of selective intrauterine growth restriction (sIUGR), 79 placents were analyzed. There were 24 placentas of TTTS and 32 placentas of normal monochorionic twins (McT) without complex twin preganancy. Placental sharing, placental cord insertion, angioarchitecture and diameter of vascular anastomosis were assessed by placental injection with colored dye and compared between TTTS and McT without complex twin preganancy. (1) Arterio-arterial (AA) anastomoses were detected in 37.5% of TTTS placentas versus 75.0% in normal McT placentas (P<0.01). (2) The median number of AA anastomoses in TTTS group was significantly less than that in normal group (0.0 vs 1.0, P<0.01). And the median total diameter of AA anastomoses in TTTS group was significantly smaller than that in normal group (0.00 vs 2.25 mm, P<0.01). (3) The incidence of placentas with at least one cord non-central insertion (70.8% vs 62.5%, P>0.05), velamentous insertion (25.0% vs 6.3%, P>0.05) in TTTS and normal McT had no difference respectively. The placental territory discordance (PTD) had no difference between TTTS and normal McT (0.33 vs 0.22, P>0.05). AA anastomosis occurs less frequently in TTTS placentas, supporting the concept of a protective role of AA anastomoses in TTTS. McT placentas without AA anastomosis have high risk for TTTS. The compensatory ablitiy of AA anastomosis may determine the time of TTTS onset. Non-central or velamentous cord insertion, placental sharing discordance are not risk factors for TTTS.

Placental characteristics of monochorionic twin pregnancy complicated with selective fetal growth restriction

Objective To evaluate the placental characteristics in monochorionic (MC) twin pregnancy with selective fetal growth restriction (sFGR). Methods Fifty-five placentas from women with MC twin pregnancy were included, who had terminated pregnancy in the Peking University Third Hospital between June 1, 2013 and June 1, 2014, including 23 cases with sFGR and 32 uncomplicated cases as control group. We perfused the placentas within 24 h after delivery, and pigment of four different colors was used to perfuse the umbilical arteries and veins of both twins and determine the types of vascular anastomosis. Umbilical cord insertion, placental territory discordance (PTD, the territory difference between two placentas/the bigger one), and the type, number and diameter of placental superficial vascular anastomosis were analyzed using two independent samples t-test, nonparametric test, χ2 test or Fisher's exact test. Results The PTD was 0.60(0.10-0.80) vs 0.22(0.00-0.90) in sFGR group and control group (Z=-3.913) respectively, and the proportion of placenta with uneven share was 91.3%(21/23) vs 50.0%(16/32) (Fisher's exact test), which were significantly higher in sFGR group (both P 0.05). The number of AA, AV and VV anastomosis in sFGR group and control group was 1.0 (0.0-2.0) vs 1.0 (0.0-4.0), 3.0 (0.0-10.0) vs 2.0 (0.0-5.0), and 0.0 (0.0-1.0) vs 0.0 (0.0-3.0) (Z= -0.256, -0.142 and -0.123); the total diameter of AA, AV and VV anastomosis was 2.7 (0.0-7.0) vs 2.2 (0.0-9.7), 4.0 (0.0-13.7) vs 3.4 (0.0-11.5), and 0.0 (0.0-7.9) vs 0.0 (0.0-7.1) mm (Z= -0.070, -0.087 and -0.087); there were no significant differences between two groups (all P>0.05). The total number of all anastomosis was 3.5 (0.0-10.0) vs 3.5 (0.0-6.0) (Z=-0.567); the total diameter of all anastomosis was 6.9 (0.0-22.4) vs 5.9 (0.0-17.1) mm (Z=-0.556); there were no significant differences between two groups (all P>0.05). Conclusions Placental sharing discordance and non-central cord insertion may be the risk factors for MC pregnancies complicated with sFGR. Key words: Pregnancy, twin; Fetal growth retardation; Placenta

Placental characteristics in uncomplicated monochorionic diamniotic twin pregnancies

Objective To investigate the association between placental sharing,vascular anastomoses,cord insertion and perinatal outcome in uncomplicated monochorionic diamniotic (MCDA) placentas.Methods Between January 1,2012 and July 31,2013,60 uncomplicated (seclective fetal growth restriction,twin anemia-polycythemia sequence and twin-twin transfusion dyndrome) MCDA placentas were studied.These uncomplicated MCDA placentas were divided into the placenta equally shared group with placental territory discordance (PTD) ＜0.25 and the placenta unequally shared group with PTD ≥ 0.25.Angioarchitecture,cord insertion type and the distance between two cord insertions were compared using the Chi-square test and nonparametric test.Results Mean maternal age was (30.3±4.1) years.There were 39 cases (65％) in the placenta equally shared group and 21 (35％) in the placenta unequally shared group.Vascular anastomoses were observed in all placentas,arterioarterial anastomoses in 58 placentas (97％),and venovenous anastomoses in 17 placentas (28％).The overall diameter and the maximum diameter of arterioarterial anastomoses in the placenta equally shared group were (0.19±0.11) cm and (0.18±0.09) cm,respectively,and were lower than those in the placenta unequally shared group [(0.27±0.11) cm and (0.27±0.12) cm,respectively] (T were-2.39 and-2.94,P＜0.05,respectively).No significant differences in the number,the overall diameter and the maximum diameter of venovenous anastomoses were observed between the two groups (all P＞0.05).The incidence of cord velamentous insertion and cord velamentous insertion plus cord marginal insertion were 14％ (11/78) and 42％ (33/78),respectively,in the placenta equally shared group,and were similar to those in the placenta unequally shared group [14％ (6/42) and 33％ (14/42),x2 were 1.00 and 0.43,P＞0.05,respectively].The mean distance between two cord insertions was shorter in the placenta unequally shared group than in the placenta equally shared group [(14.3±6.3) cm vs (18.2±6.0) cm,T=2.37,P＜0.05].Conclusions In cases with unequally shared placenta,the distance between two cord insertions is shorter and the diameter of arterioarterial anastomoses is larger,which may compensate for their unequal placental territories,leading to no complications in these MCDA twin. Key words: Twin, monochorionic; Placental circulation; Umbilical arteries; Umbilical veins

Placental sharing, birthweight discordance, and vascular anastomoses in monochorionic diamniotic twin placentas

The purpose of this study was to examine the relationship between placental territory and birthweight discordance and vascular anastomoses in monochorionic diamniotic twin placentas from pregnancies that were not complicated by twin-to-twin transfusion syndrome with 2 liveborn twins. Placentas originated from a prospective follow-up study of monochorionic diamniotic twins included in the first trimester. After injection with dyed barium sulphate, a digital x-ray angiography and high-resolution digital photograph were taken. The 2 venous territories were delineated on the angiogram. The diameter of each arterioarterial anastomosis and of each vein that participated in an arteriovenous anastomosis was measured on the digital photograph. Net transfusion over the arteriovenous anastomoses was calculated as the difference between the total venous diameters of the 2 placental parts. One hundred placentas were analyzed. Birthweight discordance increased with placental territory discordance (P < .0001). Arterioarterial diameter (P < .01), net arteriovenous transfusion (P < .001), and total anastomotic diameter (P < .01) increased with placental territory discordance. On the other hand, birthweight discordance for a given placental territory discordance decreased with increasing arterioarterial diameter (P < .01), net arteriovenous transfusion (P < .001), and total anastomotic diameter (P < .01). In unequally shared placentas, the 2 fetal circulations are more tightly linked than in equally shared placentas, which may reduce the birthweight discordance for a given placental territory discordance.

Placental sharing, birthweight discordance and vascular anastomoses in monochorionic diamniotic twin placentas

ObjectiveTo examine the relationship between the discordance in placental territory (PT), birthweight (BW), and vascular anastomoses in placentas from a prospective series of monochorionic diamniotic (MCDA) twins included in the 1st trimester.Study designCord vessels were injected with dyed barium sulphate. Rx angiograms and digital photographs of the chorionic surface were taken. BW discordance was defined as BW heavier/BW lighter twin. PT discordance was determined on Rx angiogram as the ratio of venous surface areas of the larger and smaller placental part. On the digital photograph, minimal diameters (mm) of arterio-arterial (AAs) and of each vein of an arterio-venous (AV) anastomosis were measured. An estimate of net AV transfusion was calculated as the difference of total diameters of AVs draining in either direction.Results76 placentas were analysed. BW discordance increased with PT discordance (P<0.0001). AA diameter (P<0.01) and net AV transfusion (P<0.001) towards the larger placental part increased with PT discordance. For a given PT discordance, BW discordance decreased with increasing AA diameter (P<0.01) and net AV transfusion towards the larger placental part (P<0.05).ConclusionUnequally shared placentas have larger AAs and a larger estimated net AV transfusion towards the larger placental part, as compared to equally shared placentas, which decreases BW discordance for a given PT discordance. Supported by European Commission-Eurotwin2twin - QLG1-CT-2002-01632. ObjectiveTo examine the relationship between the discordance in placental territory (PT), birthweight (BW), and vascular anastomoses in placentas from a prospective series of monochorionic diamniotic (MCDA) twins included in the 1st trimester. To examine the relationship between the discordance in placental territory (PT), birthweight (BW), and vascular anastomoses in placentas from a prospective series of monochorionic diamniotic (MCDA) twins included in the 1st trimester. Study designCord vessels were injected with dyed barium sulphate. Rx angiograms and digital photographs of the chorionic surface were taken. BW discordance was defined as BW heavier/BW lighter twin. PT discordance was determined on Rx angiogram as the ratio of venous surface areas of the larger and smaller placental part. On the digital photograph, minimal diameters (mm) of arterio-arterial (AAs) and of each vein of an arterio-venous (AV) anastomosis were measured. An estimate of net AV transfusion was calculated as the difference of total diameters of AVs draining in either direction. Cord vessels were injected with dyed barium sulphate. Rx angiograms and digital photographs of the chorionic surface were taken. BW discordance was defined as BW heavier/BW lighter twin. PT discordance was determined on Rx angiogram as the ratio of venous surface areas of the larger and smaller placental part. On the digital photograph, minimal diameters (mm) of arterio-arterial (AAs) and of each vein of an arterio-venous (AV) anastomosis were measured. An estimate of net AV transfusion was calculated as the difference of total diameters of AVs draining in either direction. Results76 placentas were analysed. BW discordance increased with PT discordance (P<0.0001). AA diameter (P<0.01) and net AV transfusion (P<0.001) towards the larger placental part increased with PT discordance. For a given PT discordance, BW discordance decreased with increasing AA diameter (P<0.01) and net AV transfusion towards the larger placental part (P<0.05). 76 placentas were analysed. BW discordance increased with PT discordance (P<0.0001). AA diameter (P<0.01) and net AV transfusion (P<0.001) towards the larger placental part increased with PT discordance. For a given PT discordance, BW discordance decreased with increasing AA diameter (P<0.01) and net AV transfusion towards the larger placental part (P<0.05). ConclusionUnequally shared placentas have larger AAs and a larger estimated net AV transfusion towards the larger placental part, as compared to equally shared placentas, which decreases BW discordance for a given PT discordance. Supported by European Commission-Eurotwin2twin - QLG1-CT-2002-01632. Unequally shared placentas have larger AAs and a larger estimated net AV transfusion towards the larger placental part, as compared to equally shared placentas, which decreases BW discordance for a given PT discordance. Supported by European Commission-Eurotwin2twin - QLG1-CT-2002-01632.

Histomorphometric Characterisation of Shared and Non-shared Cotyledonary Villus Territories of Monochorionic Placentae in Relation to Pregnancy Complications

Theoretical estimates and physiological inferences suggest that the structure of a shared cotyledon differs from a non-shared cotyledon. The aim of this study was to characterise the histomorphometry of terminal villi in shared and non-shared cotyledons in monochorionic placentae, both from uncomplicated twins and from those with twin-twin transfusion syndrome (TTTS) or discordant growth restriction (DeltaIUGR). Forty-one monochorionic placentae from Caucasian non-smokers were obtained at caesarean section. Their vascular anatomy and placental territories were ascertained by dye injection. After fixation, full thickness histological blocks were obtained by systematic random sampling from each twin's territory and the shared cotyledons. Fifty randomly selected terminal villi were assessed for: (i) median villus diameter (ii) median villus capillary diameter (iii) median fetomaternal diffusion distance (iv) median no. of capillaries/villus (v) degree of vascularization (median percentage cross-sectional area of terminal villi occupied by capillaries) using a stage micrometer and image analysis programme. The histomorphometric findings were then correlated with birthweight discordance, placental territory discordance and DeltaAVAs (no. of AVAs from smaller twin (donor) to larger twin (recipient) minus no. of AVAs from larger to smaller twin). Histomorphometric variables were similar in shared and non-shared cotyledons of uncomplicated MCDA twins. However, the median diameter of terminal villi in shared cotyledons in DeltaIUGR and TTTS placentae was significantly smaller [51.2 microm (48.2-58.3), p<0.001 and 52.6 microm (53.1-50.4), p<0.001], and had a similar number of smaller capillaries, larger fetomaternal diffusion distance and reduced vascularization compared to non-shared IUGR and TTTS placentae. However, Deltadiameter (defined as the difference between median diameters of terminal villi in large minus small twins' territories) rose with increasing birthweight discordance (Pearson correlation coefficient=0.82, p<0.001). Multiple linear regression analysis revealed that Deltadiameter was influenced by placental territory discordance (p<0.001) and birthweight discordance (p<0.01): log10 Deltadiameter=1.38+(0.01 x birthweight discordance)+(0.56 x log10 placental territory discordance) (R2=0.82, p<0.001), but there was no significant relationship with DeltaAVA and AAA. In the TTTS group, Deltadiameter correlated significantly with DeltaAVA only: log10Deltadiameter=1.44+(0.02 x DeltaAVA) (R2=0.3, p<0.001). This is the first study to characterise the histomorphometry of shared and non-shared cotyledons in MC twins. The findings suggest that abnormal placentation, rather than placental vascular anatomy may be responsible for DeltaIUGR in MC twins, whereas TTTS arises from imbalance in interfetal transfusion with resultant differing terminal villus histomorphometric features in donor, recipient and shared cotyledons.